The present invention pertains to lithium ion rechargeable batteries utilizing polymer electrolytes.
Rechargeable lithium batteries utilizing polymer electrolytes are well known see Handbook of Batteries by David Linden, (c) 1995, chapter 36. The basic structure contains a lithium anode, a polymer electrolyte, a cathode and a current collector.
Secondary, lithium-ion cells and batteries are well known in the art. One such lithium-ion cell comprises essentially a lithium-intercalatable carbonaceous anode, a lithium-intercalatable chalcogenide cathode, and a non-aqueous, lithium-ion-conducting electrolyte there between. The carbon anode comprises any of the various forms of carbon (e.g., coke or graphite) pressed into a porous conductor or bonded to an electrically conductive carrier (e.g. copper foil) by means of a suitable organic binder. A known chalcogenide cathode comprises a crystalline spinel form of manganese oxide bonded to an electrically conductive carrier (e.g., aluminum foil) by a suitable organic binder such as ethylene propylene diene monomer (EPDM).
Lithium-ion cell electrolytes comprise a lithium salt dissolved in a vehicle which may be (1) completely liquid, or (2) an immobilized liquid, (e.g. gelled, or entrapped in a polymer matrix), or (3) a pure polymer. Known polymer matrices for entrapping the electrolyte include polyacrylates, polyurethanes, polydialkylsiloxanes, polymethylacrylates, polyphosphazenes, polyethers, polyvinylidene fluorides and polycarbonates, and may be polymerized in situ in the presence of the electrolyte to trap the electrolyte therein as the polymerization occurs. Known polymers for pure polymer electrolyte systems include polyethylene oxide (PEO), polymethylene-polyethylene oxide (MPEO) or polyphosphazenes (PPE). Known lithium salts for this purpose include, for example, LiPF6, LiClO4, LiBF4, LiAsF6, LiSbF6, LiSCN, LiAlCl4, LiCF3SO3, LiN(CF3SO2)2, LiC(CF3 SO2)3, LiC2F5SO3, and LiN(C2F5 SO2)2. Known organic solvents (i.e., vehicles) for the lithium salts in carbonate, ethylene carbonate, dialkyl carbonates, cyclic ethers, cyclic esters, glymes, lactones, formates, esters, sulfones, nitriles, and oxazolidinones.
Lithium cells made from pure polymer electrolytes, or liquid electrolytes entrapped in a polymer matrix, are known in the art as xe2x80x9clithium-polymerxe2x80x9d cells, and the electrolytes therefore are known as polymeric electrolytes. Lithium-polymer cells are often made by laminating thin films of the anode, cathode and electrolyte together wherein the electrolyte layer is sandwiched between the anode and cathode layers to form an individual cell, and a plurality of such cells are bundled together to form a higher energy/voltage battery. In making such cells, it is desirable that the thin films are flexible and robust so that they can be handled without damage.
Frequently, polymer electrolytes utilized in lithium polymer batteries display high temperature instability due to the interaction of polymer binders and electrolytes resulting in dissolution and gelling. The use of such lithium polymer batteries therefore are limited in their use in starting, lighting and ignition (SLI) batteries, electric vehicle (EV) batteries, and hybrid vehicle (HV) batteries.
It is an object of the present invention to provide a chlorinated polymer based polymer electrolyte and electrodes for lithium ion rechargeable batteries. It is also an object of the present invention to provide polymer electrolytes and electrodes that are useful when operating at high temperatures.
Provided is a lithium ion rechargeable battery having a negative electrode, a positive electrode and a separator/polymer electrolyte there between comprising a chlorinated polymer. The polymer is comprised of a chlorinated polyvinyl chloride (PVC) blended with a terpolymer comprised of poly(vinylidene chloride-co-acrylonitrile-co-methyl methacrylate)s, poly(vinylidene chloride-co-methacrylonitrile-co-methyl methacrylate)s or combinations thereof.
Also provided is a negative electrode in a lithium ion rechargeable battery comprising a current collector and applied thereto a mixture of a chlorinated polymer and carbon-based materials. Also provided is a positive electrode in a lithium battery comprising a current collector and applied thereto a mixture of a chlorinated polymer and active materials.
Also provided is a separator in a lithium ion rechargeable battery, comprised of a chlorinated polymer and filler.
Also described is a lithium ion rechargeable battery comprised of (a) a negative electrode and (b) a positive electrode both comprised a current collector and applied to each, a mixture of a chlorinated polymer and active materials and (c) a separator comprised of a chlorinated polymer and filler.
Also provided is a method of manufacturing an electrode for use in a lithium ion rechargeable battery comprising preparing a mixture of a chlorinated polymer and active materials and applying the mixture to a substrate to be used as the electrode in the lithium ion rechargeable battery.
The present invention pertains to separator/polymer electrolytes and electrodes made of a chlorinated polymer useful in lithium ion batteries, preferably rechargeable lithium ion batteries.
The rechargeable lithium ion cells which use solid polymer electrolytes (SPE) or plasticized polymer electrolytes are considered to have a safety advantage over the organic liquid electrolytes because of the absence or reduced amount of a volatile, and sometimes flammable, organic solvent. In their most common forms, these cells use a lithium-ion conducting polymer membrane which acts both as the separator and as the electrolyte, carbon-containing material(s) backed by a metal current collector as the negative electrode or the anode, and transition metal oxide(s) or chalcogenide(s), blended with conductive carbon and backed by a metal current collector as the positive electrode or the cathode.
The cell reaction shown below is similar to that in a liquid organic electrolyte cell. The electrochemical process of the anode is the uptake of lithium ion during the charge and the release of lithium ion during the discharge. Therefore, the anode acts as lithium ion source whereas the cathode acts as lithium ion sink during the discharge.
Overall Reaction                     Li        x            ⁢              C        6              +                  A        y            ⁢              B        z              ⁢            ⇌      charge        discharge    ⁢            6      ⁢      C        +                  Li        x            ⁢              A        y            ⁢              B        z            
Preferably, the chlorinated PVC is blended with a terpolymer of vinylidene chloride. It showed enhanced high temperature stability and also displayed mechanical integrity in the as-cast and extracted separator films. If using vinylidene chloride terpolymer alone as the polymer binder, the as-cast separator shows good mechanical properties, but it becomes very brittle with poor handelability after the removal of plasticizer, a step used to produce porous membrane. Separately, if using chlorinated PVC alone as the polymer binder, the as-cast separator film appears to be tacky and hence limits its application. It is the blending of chlorinated PVC and terpolymer of vinylidene chloride, which provides the most desirable mechanical properties.
Chlorinated PVC is a well-known commercially available material. A number of U.S. patents describe the manufacture and use of such materials such as, U.S. Pat. No. 5,821,304; and U.S. Pat. No. 5,789,543. Preferably, the amount of chlorine is at least 57 percent bound chlorine in the polymer. Preferred chlorinated PVC resins of different molecular weights and chlorine contents are available under the name TempRite (trademark of B.F. Goodrich of Cleveland, Ohio). It is preferred that the chlorinated PVC polymer is blended with other polymeric materials. Preferred polymeric materials to be blended with the chlorinated PVC are polymers of vinylidene chloride. Even more preferred polymers are those that are terpolymers of vinylidene chloride and different terpolymers.
Vinylidene chloride and poly (vinylidene chloride) are commercially available as Saran (trademark of Dow Chemical Company of Midland, Mich.) or PVDC. The preparation of such materials is disclosed in Kirk-Othmer: Encyclopedia of Chemical Technology, Third Edition, Vol 23 (New York: John Wiley and Sons, 1983), pp 764-798.
The term xe2x80x9cPVDCxe2x80x9d means a vinylidene chloride copolymer wherein a major amount of the copolymer comprises vinylidene chloride and a minor amount of the copolymer comprises one or more unsaturated monomers copolymerizable therewith. Examples of unsaturated monomers copolymerizable with the vinylidene chloride are vinyl chloride, acrylonitrile, and alkyl acrylates having 1 to 18 carbon atoms in the alkyl group. Preferred terpolymers of vinylidene chloride are poly(vinylidene chloride-co-acrylonitrile-co-methyl methacrylate)s, poly(vinylidene chloride-co-methacrylonitrile-co-methyl methacrylate)s and combinations thereof.
The ratio of chlorinated PVC to terpolymer of vinylidene chloride ranges from about 90 to 10 percent by weight to 40 to 60 percent by weight, preferably 75/25 percent, even more preferably 50/50 percent by weight.
Electrodes are made by mixing the active materials with a suitable binder in a solvent, coating the mix onto a suitable electrically conductive support (i.e., aluminum foil) or a substrate (e.g. Mylar or paper) and removing the solvent (e.g., by heat) as is well known in the art. Various coating means including spraying, spin-coating, blade-coating, electrostatic spraying, painting and the like can be used. Some conductive carbon particles may be mixed with the active material to improve its electrical conductivity as is also well known in the art. Such electrodes will typically comprise about 3% to about 20%, by weight, binder, and about 2% to about 15%, by weight, conductive carbon particles.
The separator film in a lithium ion battery is preferably prepared from a mixture of the chlorinated polymer blend, filler and plasticizer in an organic solvent such as tetrahydroftiran (THF). Preferably, the blend of polymeric materials that is utilized for the separator may likewise be utilized for the preparation of the anode and cathode. The slurry is then cast to a desirable thickness and dried.
The anode, the negative electrode, in a lithium ion battery is preferably prepared by mixing the chlorinated polymer blend, plasticizer with carbon-based materials in THF solvent. Suitable carbon-based materials consisted of graphite, coke, soft carbon, hard carbon, microfibrous graphite, coated graphite and combinations thereof.
The cathode, the positive electrode, in a lithium ion battery is preferably prepared by mixing the chlorinated polymer blend, plasticizer with cathode active material in THF solvent. Suitable cathode active materials consisted of lithium cobalt oxides, lithium nickel oxides, lithium nickel cobalt oxides, lithium manganese oxides, vanadium pentoxide and combinations thereof.
A variety of plasticizers may be utilized in the preparation of the electrodes. Such materials that may be dialkyl (8-12 carbon atoms) esters of various polycarboxylic acids or anhydrides such as citric acid, phthalic acid, and the like. Suitable materials are as follows: Citroflex A4 (trademark of Morflex for citric acid esters), dibutyl phthalate, dioctyl phthalate, dioctyl terephthalate, dioctyl adiapate, Citroflex A2, Citroflex A6 and combinations thereof.
Electrolytic cells, such as rechargeable battery cells, are constructed by means of a lamination of electrode and electrolyte cell elements, which may be prepared from the polymer composition, such as the blend of chlorinated polymer. In the construction of the battery, a metallic current collector of foil or grid is covered with a positive electrode film or membrane, which is separately prepared as a coated layer of a dispersion of intercalation electrode composition in polymer matrix solution which is dried to form the electrode. A separator/ polymer electrolyte membrane formed as a dried coating of a composition comprising a solution of the chlorinated polymer blend, filler and plasticizer is then placed upon the positive electrode film. A negative electrode membrane formed as a dried coating of a powdered carbon dispersion in the polymer matrix solution is likewise placed upon the separator membrane layer and a current collector is laid upon the negative electrode layer to complete the cell assembly. Seeing for example U.S. Pat. No. 5,460,904 and U.S. Pat. No. 5,456,000.
Plasticizer in the laminated cells is extracted using solven Typically, the extracted cells are subjected to vacuum drying at elevated temperature to remove the undesirable moisture associated with various materials or introduced from processes. The final activation of cells is the addition of electrolyte, i. e. lithium salt dissolved in a mixture of organic solvents, and this is typically conducted inside a dry box due to the moisture sensitivity of lithium salt. Suitable lithium salts include LiPF6, LiClO4, LiBF4, LiAsF6, LiSbF6, LiSCN, LiAlCl4, LiCF3SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiC2F5SO3)2 and combinations thereof. Suitable organic so for the lithium salts include ethylene carbonate, dimethyl carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, gamma butyrolactone, methyl formate,1,2-dimethoxyethane, diethoxyethane and combinations thereof.
A particular advantage of the polymer electrolytes utilized in the lithium battery described herein is the high temperature at which the battery may be utilized such as up to 100xc2x0 C., preferably 75xc2x0 C. The chlorinated polymer blend-based polymer electrolyte system described herein, displays little or no dissolution or gelling at high temperature, namely 75xc2x0 C.